DISCUSSION ON ANIMAL TISSUE RESPIRATION 271 



permit complete recovery. Undoubtedly other accumulations and 

 disturbances occur which we have not detected. This is worthy of 

 investigation for any specific system under study. 



The Escape Phenomenon.— Where in vitro experiments are pro- 

 longed, another type of phenomenon must be borne in mind. We 

 have shown that diabetic tissue on prolonged survival in vitro grad- 

 ually regains its ability to oxidize carbohydrate. A complete restora- 

 tion takes place in four hours at 41° C, in ten hours at 37.5° C. With 

 cardiac muscle a definite elevation in the respiratory quotient of 

 normal tissue is found as early as the second hour. This change has 

 been attributed to the release of the tissue from certain influences 

 carried over from the intact animal. The change can be checked by 

 the use of other than inorganic phosphate buffers. Among these is 

 beta-glycerophosphate. In prolonged experiments with any tissue 

 this phenomenon should be borne in mind, since, it may be asso- 

 ciated, as in this instance, with an entirely different type of me- 

 tabolism toward the end of the experiment than at the start. 



Miscellaneous.— In obtaining respiratory quotients it has been our 

 experience that for vessels of any given size more reliable results 

 are obtained when the respiratory exchange is large. When the total 

 oxygen consumption and carbon dioxide production is small, the 

 results are likely to be unreliable, and generally the respiratoiy 

 quotient is erroneously high. In vessels of 20 to 24 cc. capacity, if 

 the oxygen consumption in the period of observation is less than 

 150 cmm., we are likely to obtain incorrect respiratory quotients. It 

 is recommended that for each size and type of vessel used, studies 

 be made to determine the amount of oxygen consumption that yields 

 a reliable respiratory quotient. 



COMPARISON OF SLICES AND HOMOGENIZED SUSPEN- 

 SIONS OF BRAIN TISSUE 



K. A. C. ELLIOTT 

 Institute of the Pennsylvania Hospital, Philadelphia 



Warburg introduced the technique of using slices of tissue for 

 metabolic studies, and the method has been used by many other 

 workers. Slices of many tissues can be prepared without disrupting 

 the majority of the cells; gases and substrates can diffuse in and out 

 of thin slices rapidly enough not to limit the rates of metabolic 

 processes. With various mashed and ground preparations, respiration 

 has been found to occur less rapidly, and it is commonly believed 

 that a closer approach to physiological conditions is obtained with 



